Method of manufacturing hollow drill steel



cs. A El. GUMAELHUS Riki: P53321509 OF MANUFACTURING HOLLQW DRILL STEEL Filed DIV-c 13926 Patented June 17, 1930 UNITED STATES PATENT OFFICE OLOF ABVID ENGIlLBREKT GUMAELIUS, OF OSTERBY IB RUK, SWEDEN, ASSIGNOR TO FAG-EBSTA BRUKS AKTIEBOLAG, OF FAGERSTA, SWEDEN, A COMPANY OF SWEDEN METHOD OF MANUFACTURING HOLLOW DRILL STEEL Application filed December 24, 1926, Serial No. 156,994, and in Sweden- October 9, 1926.

The manufacture of hollow drill steel has hitherto generally been performed in such a manner that a suitable filling material, for instance a more or less fine-grained material,

such as silver-sand, crushed coal or a mixture through-bored so as-to form a bottom, whereupon said hole has been closed also at the other end and the blank has been rolled so as to obtain the desired dimension, and finally the filling material has been removed.

This method entails, however, the drawback that the inner surface of the drill steel will be more or less rough or grained depending on the granulation of the filling material.

The miniature depressions thus formed in the inner surface of the drill steel constitute starting points for rust affects, which in turn soon give rise to splits caused by fatigue, and said splits constitute in turn starting points for real fractures. It should be borne in mind thata drill steel of the present kind, when used for rock drilling, is exposed to shock stresses and affects of the flush-water.

The present invention has for its object to prevent the ruining effects of said fatigue splits and consists substantially in this that a pipe consisting of iron or any other sultable metal or metal alloy is placed in a hole pre-. Viously made in the drill blank, said pipe being closed at the one end in connection with the closing of the corresponding end of the hole in the blank or independently thereof or left open at the said end, if the hole in the blank is not bored through. The said pipe is filled with a suitable material, for instance sand, and closed at the filling end, and then the rolling is performed so as to obtain the desired dimension and finally the filling material is removed' By such means the rust affects and the fatigue caused thereby are taken up by the pipe inserted in the drill steel, the starting points for the said rust afi'ects being thus located at the inner surface of the inserted pipe, the inner surface of the drill steel proper being left smooth.

which will form a thin shell after the rolling operation, is retained in the drill steel.

The pipe, which may consist of iron, metal,

or a metal alloy, as mentioned, may either fit tightly in thehole in the drill steel blank or may be coated with a medium, such as for instance a mixture of linseed oil and graphite,

which affects an adhering of the pipe to the wall of the hole and prevents the filling material from entering between the pipe and the wall of the hole at the filling operation. It is evident that, if desired, the filling material may be introduced into the pipe. before plac ing said pipe in the hole of the drill steel blank.

A11 embodiment of the invention is shown in the drawings, wherein Fig. 1 is a longitudinal section of a drill steel blank having inserted therein a core according to the invention, and Fig. 2 shows in perspective a piece of drill steel which has been rolled.

InFig. 1, A denotes the blank of drill steel which it is desired to roll. The tube B, of a suitable metal, is inserted in a hole which is I drilled in the blank, and the filling material C, for example, silver sand, is placed in the tube. The ends of the tube B are then closed in any suitable manner, for example by plugs drill steel blank, filling a metallic pipe with a suitable filling material, inserting the pipe in the holein the blank, closing the ends of the pipe, then rolling the blank until it has the desired dimensions, and then removing the filling material.

2. A method of manufacturing hollow drill steel which comprises providing a hole in a drill steel blank, inserting a metallic pipe in the hole in the blank, then filling the pipe with a suitable filling material, then elosin the ends of the pipe, then rolling the blanl until it has the desired dimensions, and then removing the filling material.

3. A method according to claim 1 in which 10 the pipe is fitted tightly into the hole in the drill steel blank.

4. A method according to claim 1 together with the step of coating the pipe before insertion into the hole in the drill steel blank 15 with a medium to cause the pipe to adhere to the walls of the said hole in the blank.

In testimony whereof I aflixt my signature.

OLOF ARVID ENGELBREKT GUMAELIUS. 

